As shown in FIG. 3, an elevator conventionally includes an elevator cage 10 tied to a balance weight 11 with a rope wound around a sheave 9. An AC motor 5 drives the sheave 9 to hoist the elevator cage 10. The illustrated control apparatus drives the AC motor 5. In the control apparatus, a three-phase alternating current from a commercial power supply 1 is full-wave rectified by a rectifier circuit 2, and converted to a direct current by a smoothing capacitor 3 further absorbing its ripple component. This converted direct current is converted by an inverter 4 to an alternating current of predetermined frequency, and input into the AC motor 5. The inverter 4 includes a plurality of semiconductor devices. A torque command from a controller 6 is input into a drive circuit 7, and the drive circuit 7 controls the conduction width (period for which a semiconductor device is on in the process of repeatedly being on (conduction)/off (interruption)) of the semiconductor devices of the inverter 4.
Regenerative energy during regenerative operation of the elevator is to be consumed by a heat dissipation circuit including a regenerating semiconductor device 12 and a power generation braking resistor 13. Specifically, during regenerative operation, the regenerating semiconductor device 12 repeatedly turns on/off in accordance with commands from the drive circuit 7, and in that process the conduction width is controlled depending on the magnitude of the regenerative energy, so that the regenerative energy will be consumed by the power generation braking resistor 13 generating heat.
If a failure of the regenerating semiconductor device 12 remaining on and not returning off, i.e. an on failure occurs, then the power generation braking resistor 13 can be overheated and cause a fire. Accordingly, in order to detect an occurrence of on failure, various safety measures have been proposed such as checking the energization state of the power generating braking resistor with a temperature sensor or the like (JP 3369890, B), checking the collector voltage of the transistor used as a regenerating semiconductor device (JP 2002-191178, A), and checking the synchronism of the base signal and collector signal of the transistor (JP 11-199148, A).
However, because all of the approaches are to detect an occurrence of on failure using hardware, there has been a problem in that the additional provision of hardware makes the device configuration complicated and also increases the cost.
Accordingly, an object of the present invention is to provide an elevating machine control apparatus configured to detect an on failure of the regenerating semiconductor device without addition of new hardware and give an appropriate safety precaution.